In a device in which slight temperature changes or tiny amounts of thermal energy is detected, a sensor that works by transducing a temperature differential generated from a signal source into an electrical signal is used. In this kind of sensors, there is a thermopile type, which detects a temperature change as thermoelectromotive force by utilizing the Seebeck effect of a thermocouple or a thermopile, which consists of a plurality of these thermocouples connected in series. Other known types of device that detect temperature changes include a pyroelectric type, which detects a change in a floating charge produced by polarization corresponding to the thermal energy of infrared rays in a base material made of ceramic or the like (this type utilizes the pyroelectric effect), and a system which detects a change in resistance produced by the heat of a temperature-sensitive resistor formed from ultrafine wire or a thin film of metal or the like (this system utilizes resistance changes) [K. Matsui, Sensa Katsuyou 141 no Jisseki Nouhau (Specific applications of actual results and know-how of 141 uses of sensors), chapter 2, CQ Publishing, 2001].
Of these, thermoelectric transducing devices that utilize the Seebeck effect are commonly used in infrared sensors, for example, because they are best for measuring temperature or for monitoring temperature differentials. The thermoelectric transducing material thin film (hereinafter referred to as thermoelectric thin film) used for these thermoelectric transducing devices is usually what is known as a metal-based thermoelectric semiconductor, which exhibits high electroconductivity and has a high Seebeck coefficient, such as bismuth (Bi), tellurium (Te), or antimony (Sb) (see, for example, Japanese Laid-Open Patent Publication No. 2000-292254).
These materials, however, are highly toxic, and furthermore there are many limitations on their film formation and working processes. In the case of the above-mentioned metal-based thermoelectric thin film materials, it is difficult to etch the film after being formed into a thin film, and it is no easy task to form a pattern by a process such as lift-off. Actually, the most common approach with these materials is to form a thin film directly by vapor deposition through a metal mask. With this process, though, it is difficult to perform finer working, and limits of width of a line to be processed make it difficult to raise the degree of integration thereof.
Similarly, SiGe is an example of a material that exhibits high thermoelectric transducing efficiency while also being easy to process and having low toxicity. SiGe-based thermoelectric materials have a long history of application, including use as a thermoelectric material in the space development, and in more recent years semiconductor thin films based on SiGe alloys have been widely used as members for devices to be used at high-temperature operations and for devices used in high-speed communications.
Known methods for manufacturing an SiGe thin film include a method in which hydrogen or GeF3 is mixed into silane (SiH4) gas, and a thin film is deposited by vacuum CVD or plasma CVD while being crystallized, and a method in which an amorphous thin film is formed on a substrate as an amorphous precursor, and this thin film is then crystallized. The former method, in which a deposited thin film is crystallized, promotes crystallization simultaneously with the formation of the thin film, but its drawbacks include the high cost of the processing equipment and the need to subject the substrate itself to a relatively high temperature of 600° C. or higher. Solid-phase growth method in which annealing is performed over an extended period is known as a type of the latter method in which an amorphous silicon thin film is first formed and then crystallized, but this method is impractical because it takes so long, and another drawback is higher manufacturing cost.
Also, when CVD is employed for forming a crystalline or amorphous semiconductor thin film, since the film contains about 2 to 20 at % hydrogen, an annealing treatment in an electric furnace is necessary to remove the hydrogen gas from the film. This process requires that annealing for degasification be performed at high temperature for an extended period, and this hampers efforts at increasing productivity, and the heat involved in the degasification treatment causes the substrate to deform, or contaminants from the substrate are diffused in the thin film, among other such problems.
One heat treatment method involves crystallizing the material by irradiating it with an excimer laser. An amorphous thin film or a polycrystalline thin film is formed on a substrate and irradiated with an excimer laser to heat and crystallize the thin film. With this technique, however, it is extremely difficult to maintain a consistent crystal quality in the thin film, and variance tends to occur in the electrical characteristics of the manufactured thin film as well.